Supported liquefied gas storage tank



Sept. 14, 1965 R. PREW SUPPORTED LIQUEFIED GAS STORAGE TANK Filed July 22, 1963 FIG. 2

FIG. I

INVENTORI FIG. 3

LIONEL R. PREW BYI W HIS ATTORN Y United States Patent SUPPORTED LIQUEFIED GAS STORAGE TANK Lionel R. Prew, Surbiton, England, assiguor to Shell Oil Company, New York, N.Y., a corporation of Delaware Filed July 22, 1963, Ser. No. 296,634 Claims priority, application Great Britain, July 24, 1962, 28,437/ 62, 28,439/ 62 7 Claims. (Cl. 220-15) This invention pertains to the construction of storage tanks. More particularly this invention pertains to the specific structure of a storage tank for liquefied gas and to apparatus for locating and supporting the walls of the tank in an external manner as to facilitate in situ construction of the tank.

In the handling of a liquefied gas at atmospheric pressure, the temperatures normally encountered are appreciably lower than the ambient temperature, for example liquefied propane and natural gas boil at atmospheric pressure at a temperature of 55 F. and 258 P. respectively. These low temperatures make it necessary for a tank for a liquefied gas to be thermally insulated from its surroundings. The necessity of thermal insulation implies that the primary barrier containing the liquid should be separate from (because it must be insulated from) the surrounding structure. In addition to such thermal insulation, it is prudent, and in the case of seagoing vessels a classification requirement, that a second barrier should be provided to guard not only against heat leakage but also against the less probable but more severe danger of actual liquid leakage through the primary barrier. Tanks constructed in the past with this double barrier have resulted in complex and cumbersome arrangement in order to achieve the characteristics required of a tank for storing and transporting liquefied gas.

Furthermore, in the construction of storage tanks which are supported by an external structure, due to the large size of the tank it is often preferable to construct the tank in situ. This is done by prefabricating the various walls of the tank; fastening the prefabricated walls to the supporting structure by means of suitable spacers; and, then joining, e.g., by welding, the various walls of the tank together. The construction of a tank in this manner, however, presents great difiiculties because the various walls of the tank have to be accurately located and supported before they are unified with each other.

It is therefore an object of this invention to provide an improved apparatus for the storage of liquefied gases.

It is another object of this invention to provide a novel construction for the walls of a storage tank for liquefied gases.

It is a further object of this invention to provide a new and improved tank for the storage of liquefied gas having a primary and a secondary barrier and which is simple in construction.

It is still a further object of this invention to provide a novel apparatus for locating and supporting the walls of a storage tank in an external structure.

It is another object of this invention to provide an apparatus for locating and supporting the walls of a storage tank so as to facilitate in situ construction of the tank.

Briefly the above objects are attained by prefabricating the walls of the storage tank from a sandwich material consisting of a primary and a secondary metal layer or barrier separated by and bonded to a corrugated sheet material and having thermal insulating material on the outer face of one of the metal layers. With walls constructed in this manner, strains in the tank due to temperature differences between the two metal layers are minimized.

The walls of the tank which are formed of the sandwich material are then located and supported in an external structure by means of brackets secured to the tank walls and which abut against a face of a horizontal sup- Patented Sept. 14, 1965 port beam mounted on the inside of the external support structure, whereby once the walls are all in place, the tank may be completed by joining the walls together.

The above objects of the invention will be more easily understood from the following description when taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a perspective view of a portion of the material used according to the invention to construct the walls of a storage tank for liquefied gases;

FIGURE 2 is a sectional view of a ship having a storage tank therein; and,

FIGURE 3 is a detailed side sectional view of the apparatus according to the invention for locating and supporting the side walls of the storage tank in the ship.

Referring now to FIGURE 1, there is shown the material from which the walls of a liquefied gas storage tank are constructed, consisting of a pair of metal sheets 1 and 2 which are separated by a rigid bracing member 3 formed from corrugated sheet material preferably having fiat sided 60 corrugations. The metal sheets 1 and 2 and the bracing member 3 are bonded together, preferably by means of a heat setting epoxy resin adhesive, to form a prefabricated sandwich material. The metal sheets 1 and 2, which form the inner and outer walls of the tank respectively are impervious to the contents of the tank and are constructed of metals, e.g., aluminum, stainless steel or nickel steel, which do not become brittle at the temperatures to be encountered by the tank.

The rigid bracing member 3 may be constructed of a corrugated sheet material which is either pervious or impervious to the contents to be stored in the tank, and may be formed from either metal, e.g., stainless or nickel steel, or non-metals, e.g., reinforced laminates. Preferably the rigid bracing member 3 consists of a corrugated sheet of polyester glass fiber reinforced laminate. Such laminates have high strength and rigidity and thermal coefiicients of expansion almost the same as steel. The corrugations in the bracing member 3 may have any desired profile. Preferably, however, the corrugations are provided with flat crests 4 in order to provide more bonding surface between the bracing member 3 and the metal sheets 1 and 2.

If it is desired to increase the thermal conductivity between the metal sheets 1 and 2, the spaces formed by the corrugated sheet material 3 can be filled with a suitable heat exchange medium which can be either a gas or a liquid. The heat exchange medium can be circulated from one side of the corrugated sheet material to the other side, i.e., between the cells defined between the bracing structure 3 and the metal sheets 1 and 2, by way of suitable connection pipes (not shown) which can be located at the tops of the walls of the tank when the corrugations of the corrugated sheet material 3 extend up and down the walls. In order, however, to permit a heat exchange medium to more readily communicate with both of the metal sheets 1 and 2, the corrugated sheet material 3 is provided with a plurality of transverse holes 5 through the sides 6 of the corrugations. The use of a heat exchange medium has the further advantage that it can be used to heat the contents of the tank or cool them as the circumstances require, for example when it is required to store a liquid in the tank at a certain temperature. If desired, the heat exchange medium can form part of a warning system for detecting leakage from the primary barrier. For instance, it can form part of a system that continuously monitors the pressure in the space between the primary and secondary barriers.

Secured to the outer surface of metal sheet 2 by any convenient means, e.g., a bituminous mastic adhesive or studs welded to the metal layer, are mats '7, covered by galvanized wire mesh 8. The mats 7 are formed from any suitable thermal insulating material such as,

glass wool, polyurethane or polystyrene foam, balsa wood faced with plywood, etc. In the event the storage tank is a free standing tank, i.e., not connected for support to any surrounding structure, then the mats '7 will cover the entire outer surface of the metal sheet 2. When the tank, however, is to be supported by a surrounding structure, the mats 7 are disposed so as to leave appropriate areas of the surface of metal sheet 2 exposed in order that the support members from the surrounding structure may be directly connected to the tank walls.

Turning now to FIGURE 2, there is shown a ship 10 having an outer hull 11 and an inner hull 12 spaced therefrom; both hulls being fabricated in the normal manner from steel plates. Inwardly spaced from inner hull 12 is a tank 13 for the storage of a liquefied gas. The tank 13 is a supported structure located and supported in the inner hull so that load strains produced in the walls of the tank can be transmitted to the structure of the ship by means of support members and load bearing thermal insulation as described hereafter. The space 14 between the hulls 11 and 12 is normally filled with ballast water. In the event of the liquid cargo coming into contact with the hull 12 due to a failure of the tank 13, the ballast water in the space 14 will help to keep the temperature of the hull 12 above the temperature at which it becomes brittle.

Referring now to FIGURE 3, there is shown a side sectional view of the apparatus for supporting and locating one of the side walls of the storage tank 13 to the ship 10. A pair of wooden beams 20, 21 which extend along the length of the side wall of the tank 13, are maintained a desired distance from a bulkhead 22 of the inner hull 12 by means of wooden spacers 23, 24 respectively, which are situated between the wooden beams and the bulkhead along the length of the wooden beams. The wooden beams 20, 21 and their respective spacers 23, 24 are secured to the bulkhead 22 by means of bolts 25, 26 respectively, which pass through the respective beams and spacers and which have their heads countersunk in the inboard faces of the wooden beams. Fastened to the inboard face of each of the beams 20, 21 is a pad of resilient material 29, 30 respectively, which may for example be fiberglass. As can be seen from the drawings, the beams 20, 21 when secured to the bulkhead 22 in the described manner, form a pair of horizontal support members or shelves which fit into the spaces left between the mats 7 fastened to the outer surface of the metal sheet 2.

In order to properly position the wall of the tank with respect to the beams 20, 21, a supporting bracket 31 is provided. The bracket 31 is in the form of an angle iron having one of its flanges 32 welded to the metal sheet 2. When the wall is properly positioned, the flange 33 of bracket 31 will abut against the upper surface of the beam 20, and the pads 29 and 30 bear respectively against the fastened flange 32 of the bracket 31 and the metal sheet 2.

A simple spring catch 34 is provided in order to latch the wall of the tank in its proper position. The spring catch 34 consists of a plate of spring steel which is secured to the bolt 26 between the beam 20 and the spacer 24 and has a downwardly and outwardly bent portion adapted to engage a lip 35 on the bracket 31 when the wall of the tank has been properly positioned relative to beams 20 and 21.

In order to construct a tank according to the invention in situ, a plurality of prefabricated panels corresponding to the walls and top and bottom of the tank are prepared. The panels corresponding to the top and walls of the tank are fabricated as shown in FIGURE 1 and are provided with support brackets 31. The bottom of the tank is fabricated similar to the structure shown in FIG- URE 1 with the exception that the glass wool mats 7 are replaced by a layer of polyurethane foam which completely covers the surface of metal sheet 2.

The fabrication of the tank in situ is begun by first simply laying the panel corresponding to the bottom of the tank on the lower portion of the inner hull 12 with the polyurethane foam layer acting as a load bearing thermal insulating layer and a means of transmitting cargo loads to the inner hull 12. The panels correspond ing to the top and side walls of the tank are then positioned in their proper places by positioning the flanges 33 of brackets 31 along the upper surfaces of their corresponding beams 20 and exerting pressure of the panels so as to push them toward the inner hull. As the forward edges of the brackets 31 engage the catches 34, the resilient pads 29 and 30 are compressed. Eventually, the catches 34 pass over the upper edge of the lips 35 and spring into place thereby locking the brackets 31 and hence the top and side walls of the tank in their proper positions. The positioned brackets 31 are maintained in contact with the catches 24 by the pressure exerted by the resilient pads 29, 30 which are still under compression and attempting to expand. Once the various panels are positioned the fabrication of the tank may be completed by welding the various panels together.

Obviously various modifications and variations of the invention, as herein described, may be made without departing from the spirit and scope of the invention. For example, the wall supporting apparatus could be used for locating and positioning tank walls which are designed for use in storing liquids other than liquefied gases. Therefore, only such limitations as are indicated in the appended claims should be imposed.

I claim as my invention:

1. Apparatus for supporting and maintaining a liquefied gas storage tank in a fixed spaced relationship to a rigid external structure comprising:

at least one horizontal wooden beam extending along the length of each of the walls of said tank, said wooden beams being rigidly fastened to the inner surface of said external structure;

a resilient material mounted on the surface of said beams which face said tank walls with said resilient material abutting against said tank walls;

a bracket means rigidly fastened to and extending laterally from each of said walls of said tank, each of said bracket means abutting against the upper surface of the adjacent one of said wooden beams; and

means for latching said bracket means in place against said wooden beam so that said resilient material is in a state of compression, whereby said tank walls are completely supported in a fixed spaced relationship to said rigid external structure.

2. Apparatus for supporting and maintaining the walls of a tank in spaced relationship to a rigid external structure comprising:

a pair of vertically displaced horizontal Wooden beams extending along the length of each of said walls of said tank, each of said wooden beams being rigidly fastened at intervals along its length to the inside of said external structure and separated therefrom by wooden spacers;

an angle iron for each of said walls, each of said angle irons having a first flange secured to one wall of said tank and its other flange extending laterally from said tank Wall and abutting against the upper surface of the lower of the pair of wooden beams adjacent the respective tank wall;

means for latching said laterally extending flanges in place against said wooden beams; and

a layer of resilient material mounted on the surface of said wooden beams facing said tank walls, said resilient material abutting against said tank walls and being in a state of compression when said bracket means are latched in place.

3. The apparatus of claim 2 wherein said laterally extending flange is provided with an upward extending lip; and wherein said latching means comprises a sheet of spring steel fastened to the upper of said Wooden beams and adapted to engage said lip.

4. The apparatus of claim 3 wherein said external rigid structure is a ship.

5. The apparatus of claim 3 wherein said tank walls are constructed of a pair of parallel metal sheets separated by a rigid bracing structure formed from corrugated sheet material, said metal sheets being adhesively bonded to said rigid bracing structure whereby a plurality of cells are defined between said bracing structure and said metal sheets; and, a thermal insulating material mounted on the surface of said tank walls facing said rigid external structure.

6. The apparatus of claim 5 including a fluid heat exchange medium filling said cells.

7. The apparatus of claim 5 wherein said bracing structure contains perforations permitting communications between said plurality of cells.

References Cited by the Examiner UNITED STATES PATENTS Brun 220-9 Brown 220-15 Hasenburger 20-4 Wagner 220-15 X Beckwith 220-9 Clark et al. 220-15 Kurkovich 220-15 Leroux 220-9 Brown 220-9 Bergman 220-15 Schlnmberger 220-9 Dosker 220--15 THERON E. CONDON, Primary Examiner.

2o GEORGE O. RALSTON, Examiner. 

1. APPARATUS FOR SUPPORTING AND MAINTAINING A LIQUEFIED GAS STORAGE TANK IN A FIXED SPACED RELATIONSHIP TO A RIGID EXTERNAL STRUCTURE COMPRISING: AT LEAST ONE HORIZONTAL WOODEN BEAM EXTENDING ALONG THE LENGTH OF EACH OF THE WALLS OF SAID TANK, SAID WOODEN BEAMS BEING RIGIDLY FASTENED TO THE INNER SURFACE OF SAID EXTERNAL STRUCTURE; 